CROSS-REFERENCE TO RELATED APPLICATION
BACKGROUND OF THE INVENTION
The present invention claims the benefit of commonly-owned, co-pending U.S. Provisional Patent Application Ser. No. 60/408,956 filed Sep. 6, 2002, and is related to U.S. patent Publication Nos. 2002/0194570, 2002/0191712, 2002/0181581, filed on Apr. 22, 2002, Apr. 9, 2002, Feb. 19, 2002, respectively, and to the co-pending, commonly-assigned patent application entitled “PACKET INSERTION MECHANISM FOR AN IMPROVED ATSC DTV SYSTEM,” filed on ______, the entire contents and disclosure of each of which are incorporated by reference as if fully set forth herein.
1. Field of the Invention
- DISCUSSION OF THE PRIOR ART
The present invention relates to a digital signal transmission system and particularly to the transmission of a signal representative of encoded digital data.
The ATSC standard for high-definition television (HDTV) transmission over terrestrial broadcast channels uses a signal that comprises a sequence of twelve (12) independent time-multiplexed trellis-coded data streams modulated as an eight (8) level vestigial sideband (VSB) symbol stream with a rate of 10.76 MHz. This signal is converted to a six (6) MHz frequency band that corresponds to a standard VHF or UHF terrestrial television channel, over which the signal is broadcast at a data rate of 19.39 million bits per second (Mbps). Details regarding the (ATSC) Digital Television Standard and the latest revision A/53 are available at http://www.atsc.org/.
While the existing ATSC 8-VSB A/53 digital television standard is sufficiently capable of transmitting signals that overcome numerous channel impairments such as ghosts, noise bursts, signal fades and interferences in a terrestrial setting, receiving antennas have increasingly been placed indoors, adding to the challenge of delivering a clear signal. There accordingly exists a need for flexibility in the ATSC standard so that streams of varying priority and data rates may be accommodated.
To address these concerns, the present inventors have disclosed enhancements to the A/53 transmitter in U.S. patent Publication Nos. 2002/0194570 (hereinafter “the '570 application”), 2002/0191712 (hereinafter “the 712” application”), 2002/0181581 (hereinafter “the 581 application”) and “PACKET INSERTION MECHANISM FOR AN IMPROVED ATSC DTV SYSTEM” (hereinafter “the Packet Insertion application”) whose disclosures have been incorporated by reference herein.
- SUMMARY OF THE INVENTION
The present invention is directed to further improvements relating to signal transmission quality and to efficient leverage of existing A/53 infrastructure.
In one aspect, the present invention concerns the encoding of parameters to be embodied within a television broadcast signal for transmission.
In another aspect, the present invention relates to techniques for encoding into a signal parameters to be transmitted and which are needed by a wireless receiver both to correctly ascertain the transmitted signal and to decode data accompanying the parameters in the signal.
In yet another aspect, the present invention concerns leveraging data structures in a standard television protocol to accommodate enhancements to the standard that retain compatibility with existing receivers.
In accordance with preferred embodiments of the invention, there is provided wireless communication of a leading bit string comprising a header and a body, and a trailing bit string comprising a header and a body. For example, a bit string of length N may have a header X0, X1, . . . XK and a body XK+1, XK+2, . . . XN−1. Data is encoded to form the body of the leading bit string. The header of the trailing bit string is formed to include at least one bit of a parameter to be used by a receiver in decoding the encoded data. A wireless signal representing at the receiver the leading bit string and then the trailing bit string is transmitted to the receiver.
BRIEF DESCRIPTION OF THE DRAWINGS
The encoding techniques preferably include applying a fixed code to encode bits of a bit-stream, one-by-one, to create an encoded bit-stream. The encoded bit-stream is modulated to produce a signal whose frequency range at any given time is predetermined independently of the code. The signal, thus modulated, is transmitted within the frequency range.
Details of the invention disclosed herein shall be described below, with the aid of the figures listed below:
FIG. 1 illustrates a block diagram of an exemplary television communication system according with the present invention;
FIG. 2 is a diagram of a circuit used for encoding parameters in the system portrayed in FIG. 1; and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 3 is an exemplary flow diagram representative of processing that data for transmission undergoes in the system of FIG. 1 prior to transmission and after reception.
FIG. 1 depicts an exemplary embodiment of television communication system 100 in accordance with the invention. The communication system 100 includes an encoder 104, a transmitter 108, a receiver 112 and a data decoder 116. The encoder 104 includes a data encoder 120, which receives a parameter bit-stream 124 and a data bit-stream 128, and a parameter encoder 132. The transmitter 108 is communicatively connected to the encoder 104 and has a modulator 136 and an antenna 140. The receiver 100 an antenna 144 configured for wireless reception of signaling from the antenna 140. The receiver 100 further includes a demodulator 148, a parameter decoder 152 and an equalizer 156, and is communicatively connected with the data decoder 116.
FIG. 2 illustrates an example of a sequence generator 200 utilized for bit encoding in accordance with the present invention. The sequence generator 200 includes a four element shift register 204, which has four delay elements such as D flip-flops 208, 212, 216, 220. An exclusive-OR gate tap 224 is disposed between the third element 216 and the fourth element 220. The fourth element 220 has an output terminal 228 which feeds back to an input terminal 232 of the first element 208 and to the tap 224.
As shown in FIG. 2, each of the flip-flops 208-220 has a pre-loaded bit value and is connected to a common clock (not shown). With the first clock pulse, for example, the output “0” on the fourth flip-flop 220 feeds back to first flip-flop 208. On that same pulse, the value “1” of the first flip-flop 208 shifts forward to the second flip-flop 212. Likewise, the value “0” on the second flip-flop 212 shifts forward to the third flip-flop 216. Again, on that same pulse, the value “0” of the third flip-flop 216 is exclusively-ORed with the output “0” to shift the result, “0”, to the fourth flip 220. Accordingly, after the first clock pulse, the register contents have changed from “1000” to “0100”. Each subsequent clock pulse changes the register contents, and the sequence starts to repeat after 15 clock pulses. The pre-load followed by 14 clock pulses generates at the output 228 the sequence “000111101011001” which repeats for each subsequent 15 clock pulses. This sequence is a linear recursive sequence, i.e., a periodic sequence of bits generated by shift register with feedback. The above sequence is used in the present invention as a fixed code. In particular, the fixed code is applied to each bit of data to be encoded to produce the same 15-bit fixed code if the bit is zero, or the opposite of the code, i.e., with zeroes becoming ones and ones becoming zeroes, if the bit is one. This can be implemented by, for example, connecting the output 228 and the bit to be encoded to an XOR gate, and the resulting output and the bit value “1” to another XOR gate. Advantageously, the sequence “000111101011001” can be reliably detected at the receiver, because it minimally correlates with a shifted version of itself. In an alternative implementation, the sequence generator 200 can include an additional XOR gate tap between the first element 208 and the second element 212 that is fed by the output 228. Also, pre-load values other than “1000” can be used. Nor is a sequence generator in accordance with the invention limited to four delay elements. It is further within the intended scope of the invention for the sequence generator 200 to be implemented with an XOR gate or gates in the feedback path rather than embedded within register 204.
FIG. 3 is an exemplary flow diagram which shows one example of the processing of the parameter and data bit-streams 124, 128 in the digital television communication system 100. A frequency range of the signal for transmission is determined (304) and may, alternatively, be determined at any point before modulation of the signal for transmission. The frequency range of the signal may also be changed or varied, for example in accordance with the type of data being processed, although it is predetermined independently of the fixed code. In step 308, a fixed code is determined, although it can be determined any time before encoding.
If there is no data for transmission (312), processing waits.
Otherwise, if the parameter bit-stream 124 is ready for reception by the data encoder 120, it is received (316). The parameter bit-stream 124 is time-synchronized with the data bit-stream 128, and may therefore not be ready for reception if the data bit-stream is not ready. In addition, no parameters may be ready for reception if parameters have not changed, since parameters for the system 100 do not necessarily change in any particular time period. If the parameter bit-stream 124 is received, its bits are encoded bit-by-bit, one bit at a time, by the parameter encoder 132 using the fixed code (320). A predetermined number of encoded bits are used in forming the headers of two bit strings before a new bit string pair is utilized, each bit string consisting of two parts, a header and a body. One of the two bit strings is a leading bit string and the other one is a trailing bit string. Specific ones of the encoded parameters are allotted the leading bit string header and the other parameters are allotted to the trailing bit string header (324).
Meanwhile, if the data bit-stream 128 is ready for input, it is received (328) and encoded (332). Although the parameter bit-stream 124 is preferably encoded bit-by-bit, one bit at a time, encoding of the data bit-stream would not typically be subject to such restrictions. The data bit-stream 128 is a video interlaced signal, and, as such, represents a frame which divides into two fields, an even field and an odd field. Encoded data from one of the fields is used in forming the body of a leading bit string. Similarly, encoded data from the other field is used in filling the body of a trailing bit string (336). Processing of the data and parameter bit-streams 124, 128 is synchronized so that each of the two types of bit strings receives its respective encoded data and encoded parameters that correspond to that data. In one embodiment, although the encoded parameters for a frame are divided into two groups for forming their respective field headers, the encoded parameters apply to the encoded data of the entire frame.
A carrier signal is then modulated by the modulator 136 using the encoded bit string pair for wireless transmission of a signal representing at the receiver the leading bit string and then the trailing bit string (340).
The received signal is demodulated by the demodulator 148 (344), and parameters are decoded by the parameter decoder 152 (348).
The parameters define the number of discrete levels in the digital wireless signal conveying the bit-streams 124, 128, and are therefore used by the equalizer 156 in resolving multipath or otherwise converging the signal (352). The decoded parameters are also utilized in decoding the data bit-stream 128 (356).
The inventive television communication system 100 can be implemented to enhance an A/53 system proposed by the current inventors and described in the Packet Insertion application.
The Packet Insertion application discusses the use of the following parameters in a parameter bit-stream.
|TABLE 1 |
|Parameter Definitions |
|Parameter || ||Number |
|Name ||Definition ||of bits |
|MODE ||Modulation type (2-VSB, E-VSB etc) ||2 |
|NRS ||Presence of Backward Compatible Parity Byte ||1 |
| ||Generator (BCPBG) |
|NRP ||Number of robust packets before encoding ||4 |
|TR ||Coding Rate ||1 |
The parameters convey the number of levels in the transmitted signal, and since this information is used by the equalizer, the parameters must be decoded before equalization. Therefore, robust methods that can survive severe channel conditions are needed. The present invention expands on the '570 techniques of transmitting these parameters to the receiver in a reliable manner.
In accordance with the A/53 standard, the header of each field contains an 832-bit “data field sync” of specific format. The format includes a 92-bit reserved area (corresponding to symbol numbers 729-820) which the standard recommends be filled with repeated information for extra redundancy.
As shown above in TABLE 1, 8 parameter bits need to be transmitted. Encoding by the sequence generator of FIG. 2
yields 8×15=120 bits, a total which exceeds the 92 bits of reserved space. The inventive technique splits the encoded bits between the two fields of a frame, e.g. 4 bits allocated per field. An extra parity bit is added to each group of 4 bits for an additional level of error detection, bringing the total to 5 bits, or 5×15=75 encoded bits, per field. TABLE 2 below defines the symbols 729-820 for odd and even fields.
|TABLE 2 |
|Symbol definitions in Field sync |
|Symbol Number ||Even (odd) Held sync ||Odd (even) field sync |
|729-743 ||LSB of MODE ||bit0 (LSB) of NRP |
|744-758 ||MSB of MODE ||bit1 of NRP |
|759-773 ||MRS ||bit2 of NRP |
|774-788 ||TR ||bit3 (MSB) of NRP |
|789-803 ||Parity bit ||Parity bit |
|804-820 ||Reserved ||Reserved |
As set forth more fully in the Packet Insertion application, if MODE=0, the rest of the parameters are not utilized. Receivers adapted for the enhancements by the current inventors can decode the MODE parameter to identify whether the received signal embodies the enhanced bit-stream formats, and, if so, can decode the other parameters.
While there have been shown and described what are considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.